1. Field of the Invention
The present invention generally relates to a plane light source structure, and more particularly to a plane light source structure for planar display.
2. Description of the Prior Art
Typically, plane light source is always for liquid crystal display devices. Plane light source projected from rear end of the liquid crystal display devices is called back light source, while plane light source projected from the front side of the liquid crystal display devices is called front light source. Liquid crystal display devices using back light source are called transmissive-type, while using front light source are called reflective-type. No matter the transmissive-type or reflective-type liquid crystal display devices are used, a high brightness and stable light source is necessary.
A conventional transmissive-type liquid crystal display device, as shown in FIG. 1, has a flat light guide plate 102 that is used to guide light rays from two light sources 104-1 and 104-2 at the two opposite ends of the light guide plate 102 to light-emitting surface thereof and to liquid crystal panel. There are many convex/concave dots on the bottom of the light guide plate 102 in FIG. 1 to reflect light rays to the upper side. Another way for reflecting upward light rays is to utilize a plurality of slanted portions (V-cuts). A reflector 106 below the opposite surface of light-emitting surface of the light guide plat 102 reflects all refractive downward light rays to the light-emitting surface of the light guide plate 102. A polarizing plate 108 and a lower substrate 110 are sequentially on the light guide plate 102. The material of conventional lower substrate 110 uses transparent glass, which thin film transistors 112 are directly formed thereon. A passivation layer 114 and transparent electrodes 116 are formed sequentially on the lower substrate 110 to form a lower plate of the liquid crystal panel. Next, a color filter 122 and transparent electrodes 120 are formed sequentially on another transparent glass, which is upper substrate 124 of the liquid crystal panel, to form upper plate of the liquid crystal panel. Then, upper plate and lower plate are sealed with transparent electrode layers 116, 120 face to face and vacuumed, and liquid crystal 118 is injected into the space between the upper and lower plates to form the liquid crystal panel. Finally, a polarizing plate 126 is placed on the upper substrate 124 to form a transmissive-type liquid crystal display device 100. Transmissive-type liquid crystal display devices are usually for television or monitor of a computer, especially for large-scale display devices.
The light guide plate 102 in FIG. 1 is flat. However, there is another type light guide plate, such as the wedge light guide plat 103, as shown in FIG. 2. Reflecting light manner of the wedge light guide plate 103 can only use a plurality of slanted portions (V-cuts) to guide the light rays to the light-emitting surface vertically. It has an advantage for the wedge light guide plate 103 that only single light source 104 is needed.
As shown in FIG. 3, a technique of hollow light guide plate announced by Fujitsu is disclosed. Light rays from a plurality of light sources 202 passing through mirrors 204 enter reflection zone in-between. There are four control plates 206 in the reflection zone to guide light rays to light-emitting surface appropriately. Reflectors 208 are located below the control plates 206 to reflect light rays back to the light-emitting surface. Finally, light rays illuminate liquid crystal display panel through the lenses 210. This kind of plane light source structure is very complicated, and will not be used due to manufacturing cost as well as yield.
Another conventional reflective-type liquid crystal display device is shown in FIG. 4, wherein light guide plate 102 is located on the liquid crystal display panel, and thin film transistors 112 are formed on the lower substrate 110 directly. A passivation layer 114 and a reflective film 115 are formed on the lower substrate 110 sequentially to form so called lower plate of the liquid crystal display panel. Then, color filter 122 and transparent electrode layer 120 are formed on another transparent glass, which is upper substrate 124 of the liquid crystal display panel, to form so called upper plate of the liquid crystal display panel. The transparent electrode layer of the upper plate and the reflective film of the lower plate are sealed face to face and vacuumed, and then liquid crystal 118 is injected into the space between the upper and lower plates to form the so called liquid crystal display panel. A retardation film 127, a polarizing plate 126, and a light guide plate 102 are sequentially on the upper substrate 124. A light source 104 is at one end surface of the light guide plate 102. The retardation film 127 is to retard phase of incident light usually by quarter wavelength, and called retardation film of quarter wavelength.
The light source of reflective-type liquid crystal display device is on the front side of liquid crystal display panel, and also called front light source. Light rays from the light source 104 are guided downward by the light guide plate 102 and reflected upward to user by reflective film 115. Reflective-type liquid crystal display devices are usually used for display panel of watches or mobile phones, especially for small-scale display devices.
Planar display devices now are toward to minimized volume and reduced weight. It is difficult to achieve minimized volume of the planar display devices, and particularly to apply the planar display devices to dual display module. Moreover, light rays in the liquid crystal panel pass through many media, and energy of the light rays is substantially lost. Illumination of light rays emitted from the light source is thus decreased when the light rays are received by eyes of user. It is necessary to develop another planar display device that can minimize volume, reduce weight of the display device and increase illumination of light rays.